Zhaojun Nie

Xylem transport and gene expression play decisive roles in cadmium accumulation in shoots of two oilseed rape cultivars (Brassica napus).

Cadmium (Cd) is a toxic metal which harms human health through food chains. The mechanisms underlying Cd accumulation in oilseed rape are still poorly understood. Here, we investigated the physiological and genetic processes involved in Cd uptake and transport of two oilseed rape cultivars (Brassica napus). L351 accumulates more Cd in shoots but less in roots than L338. A scanning ion-selective electrode technique (SIET) and uptake kinetics of Cd showed that roots were not responsible for the different Cd accumulation in shoots since L351 showed a lower Cd uptake ability. However, concentration-dependent and time-dependent dynamics of Cd transport by xylem showed L351 exhibited a superordinate capacity of Cd translocation to shoots. Additionally, the Cd concentrations of shoots and xylem sap showed a great correlation in both cultivars. Furthermore, gene expression levels related to Cd uptake by roots (IRT1) and Cd transport by xylem (HMA2 and HMA4) were consistent with the tendencies of Cd absorption and transport at the physiological level respectively. In other words, L351 had stronger gene expression for Cd transport but lower for Cd uptake. Overall, results revealed that the process of Cd translocation to shoots is a determinative factor for Cd accumulation in shoots, both at physiological and genetic levels.

Antioxidant enzyme systems and the ascorbate–glutathione cycle as contributing factors to cadmium accumulation and tolerance in two oilseed rape cultivars (Brassica napus L.) under moderate cadmium stress

Oilseed rape (Brassica napus L.) with high tolerance to cadmium (Cd) may be used in the phytoremediation of Cd-contaminated fields. However, the mechanisms responsible for Cd accumulation and tolerance in oilseed rape are still poorly understood. Here, we investigated the physiological and molecular processes involved in Cd tolerance of two oilseed rape cultivars with different Cd accumulation abilities. The total Cd accumulation in cultivar L351 was higher than cultivar L338, particularly with increasing concentrations of Cd exposure. L338 was a more pronounced Cd-sensitive cultivar than L351, while higher activities of antioxidant enzymes (CAT, APX, GR, DHAR) as well as higher contents of GSH and AsA were all observed in L351 under Cd treatments, especially at high levels. No differences were found in SOD activities between the two cultivars under the same Cd treatments, suggesting that SOD was not the key factor in relation to the differences of Cd tolerance and accumulation between them. Gene expression levels of BnFe-SOD, BnCAT, BnAPX, BcGR and BoDHAR in roots of L351 were relatively higher than that in L338 under Cd exposure as well as BnCAT and BcGR in leaves. It is concluded that antioxidant enzymes and the ascorbate-glutathione cycle play important roles in oilseed rape Cd accumulation and tolerance.

INTERACTION OF MOLYBDENUM AND PHOSPHORUS SUPPLY ON UPTAKE AND TRANSLOCATION OF PHOSPHORUS AND MOLYBDENUM BY BRASSICA NAPUS

A hydroponic trial was conducted to assess interaction of molybdenum (Mo) and phosphorus (P) on uptake and translocation of P and Mo by Brassica napus. Molybdenum was applied at four rates (0, 0.01, 0.1 and 1 mg L−1) and P at three rates (1, 30, and 90 mg L−1) in nutrient solution. The results indicated that P increased shoot growth and 0.01 mg L−1 Mo improved the growth of shoots and roots. Molybdenum increased shoot P uptake and root P concentration and uptake when higher P was provided, and had a stimulating effect on P translocation from shoots to roots. P increased shoot Mo concentration and uptake, decreased those in roots, and enhanced Mo transport from roots to shoots. These results implied that both Mo and P had beneficial effects on Mo and P absorption and translocation and co-application of them were necessary to promote growth and utilization of Mo and P for Brassica napus.

Effects of Molybdenum and Phosphorus Fertilizers on Cold Resistance in Winter Wheat

A pot trial with acid yellow-brown soil was conducted to investigate the effects of molybdenum (Mo) and phosphorus (P) fertilizers on cold resistances of winter wheat. Molybdenum was applied at two rates (0 and 0.15 mg Mo kg−1 soil) and P at four rates [0, 100, 200, and 300 mg phosphorus pentoxide (P2O5) kg−1 soil] in experiment 1. Both Mo and P fertilizers were applied at two rates (0 and 0.15 mg Mo kg−1 soil; 0, 150 mg P2O5 kg−1 soil) in experiment 2. Seed yield, soluble sugar, water-soluble protein, ascorbic acid (AsA), malondialdehyde (MDA), and abscisic acid (ABA) concentrations were studied. The results indicated that Mo and P fertilizer increased seed yield, soluble sugar, water-soluble protein, and AsA but decreased the MDA. It implied that appropriate Mo applied with P application had beneficial effects on increasing seed yield and enhancing the cold resistance ability through changing biological substances concentration in winter wheat.